Rock Fragments in Trichloroethene Microcosms for Bedrock Aquifers

The purpose of this study was to evaluate microcosm methods that can be used to predict the in situ anaerobic reductive dechlorination of trichloroethene (TCE) in bedrock aquifers with and without amendments. Microcosm conditions (e.g., surface area:volume ratio, initial TCE concentration [C ₀], incubation temperature) were selected to simulate in situ conditions at the site. The effect of rock media in the microcosms as a source of surface area and nutrients was also assessed. Comparison was made between microcosms constructed with sterile rock media and rock media submerged for 45 days in a groundwater well within a TCE plume for field colonization. Statistically significant biotic degradation of TCE was observed in microcosms with both groundwater only and non-field-colonized rock media, when amended with lactate. Measured half-lives were similar to half-lives observed in field conditions. Normalizing biotic results to abiotic results provides a method that deducts the abiotic losses and allows complete comparison between sample rounds, assuming samples were randomly selected for analysis within the sample round to avoid systematic errors or variation.     

Complete dechlorination of tetrachloroethene to ethene in presence of methanogenesis and acetogenesis by an anaerobic sediment microcosm

An anaerobic consortium taken from brackish sediments, enriched byPCE/CH₃OH sequential feeding, was capable of completely dechlorinating tetrachloroethene(PCE) to ethene (ETH). In batch experiments, PCE (0.5 mM) was dechlorinated to ethene (ETH) in approximately 75 h with either CH₃OH or H₂ as the electron donor. When VC (0.5 mM) was added instead of PCE it was dechlorinated without any initial lag by the PCE/CH₃OHenriched consortium, although at a lower dechlorination rate. In batch tests H₂ could readilyreplace CH₃OH for supporting PCE dechlorination, with a similar PCE dechlorination rate andproduct distribution with respect to those observed with methanol. This indicates that H₂ productionduring CH₃OH fermentation was not the rate-limiting step of PCE or VC dechlorination.Acetogenesis was the predominant activity when methanol was present. A remarkable homoacetogenicactivity was also observed when hydrogen was supplied instead of methanol.     

Microbial composition of chlorinated ethene-degrading cultures dominated by Dehalococcoides

The community composition of microbial cultures degrading tetrachloroethene (PCE), trichloroethene (TCE), cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC) to ethene was studied. A combination of PCR-denaturing gradient gel electrophoresis (PCR-DGGE) and 16S rRNA gene sequence analysis revealed that all cultures contained Dehalococcoides populations, but that the populations of other organisms varied widely. Based on the sequences of cloned 16S rRNA genes, real-time PCR methods were developed for several of these phylotypes affiliated with the putative dechlorinators Sulfurospirillum and Geobacter, the putative methanogens Methanomethylovorans, Methanomicrobiales, Methanosaeta and Methanosarcina, the putative acetogens Acetobacterium, Spirochaetes, and Sporomusa, and the putative fermenters Bacteroidetes, Syntrophus, and Syntrophobacter. These novel quantitative PCR methods were then used to estimate relative abundances of each phylotype in several individual cultures maintained on each chlorinated ethene. Dehalococcoides populations were the dominant phylotypes assayed in most KB-1 cultures, agreeing with the DGGE and cloning results. A Geobacter phylotype was also strongly represented in most PCE and TCE cultures, but not in cDCE or VC cultures, suggesting a possible role for this organism as a PCE-to-cDCE dechlorinator. The Sulfurospirillum phylotype was estimated to comprise a minor fraction of 16S rRNA gene copies and did not appear to have an important role in dechlorination.     

Anaerobic Microbial Reductive Dehalogenation of Chlorinated Ethenes

The current knowledge on microbial reductive dechlorination of chlorinated ethenes (CEs) and its application are discussed. Physiological studies on CEs dechlorinating microorganisms indicate that a distinction can be made between cometabolic dechlorination and halorespiration. Whereas cometabolic dechlorination is a coincidental and nonspecific side reaction, catalyzed by several methanogenic and acetogenic bacteria, halorespiration is a specific enzymatic reaction from which metabolic energy can be gained. In contrast to the well-studied biological dechlorination of PCE to cis-DCE, little is known about the biology of the further dechlorination from cis-DCE to ethene. Bacteria performing the latter reaction have not yet been isolated. Microbial reductive dechlorination can be applied to the in situ bioremediation of CEs contaminated sites. From laboratory and field studies, it has become clear that the dechlorination of tetrachloroethene (PCE) to cis-clichloroethene (cis-DCE) occurs rapidly and can be stimulated relatively easily. However, complete reduction to ethene appears to be a slower process that is more difficult to achieve.     

Anaerobic dechlorination of trichloroethene,tetrachloroethene and 1,2-dichloroethane by an acetogenic mixed culture in a fixed-bed reactor

An anaerobic enrichment culture with glucose as the sole source of carbon and energy plus trichloroethene (TCE) as a potential electron acceptor was inoculated with material from a full size anaerobic charcoal reactor that biologically eliminated dichloromethane from contaminated groundwater (Stromeyer et al. 1991). In subcultures of this enrichment complete sequential transformation of 10 µM TCE viacis-dichloroethene and chloroethene to ethene was reproducibly observed. Maintenance of this activity on subcultivation required the presence of TCE in the medium. The enrichment culture was used to inoculate an anaerobic fixed-bed reactor containing sintered glass Raschig elements as support material. The reactor had a total volume of 1780 ml and was operated at 20 °C in an up-flow mode with a flow rate of 50 ml/h. It was fed continuously with 2 mM glucose and 55 µM TCE. Glucose was converted to acetate as the major product and to a minor amount of methane; TCE was quantitatively dehalogenated to ethene. When, in addition to TCE, tetrachloroethene or 1,2-dichloroethane were added to the system, these compounds were also dehalogenated to ethene. In contrast, 1,1,1-trichloroethane was not dehalogenated, but at 40 µM severely inhibited acetogenesis and methanogenesis. When the concentration of TCE in the feed was raised to 220 µM, chloroethene transiently accumulated, but after an adaptation period ethene was again the only volatile product detected in the effluent. The volumetric degradation rate at this stage amounted to 6.2 µmol/l/h. Since complete transformation of TCE occurred in the first sixth of the reactor volume, the degradation capacity of the system is estimated to exceed this value by factor of about ten.Abbreviations CA chloroethane - 1,1-DCA 1,1-dichloroethane - 1,2-DCA 1,2-dichloroethane - 1,1-DCE 1,1-dichloroethene - c-DCE cis-1,2-dichloroethene - t-DCE trans-1,2-dichloroethene - PCE tetrachloroethene, perchloroethene - 1,1,1-TCA 1,1,1-trichloroethane - TCE trichloroethene - VC chloroethene, vinyl chloride     

Evaluation of Three Electron-Donor Permeable Reactive Barrier Materials for Enhanced Reductive Dechlorination of Trichloroethene

Understanding the fate of complex electron-donor materials is important for developing efficient biostimulation strategies to treat ground water contamination by chlorinated ethenes (CEs). The fermentation product distributions and H₂ production of common permeable reactive barrier (PRB) carbon substrates (dairy whey, sodium lactate syrup, and Hydrogen Release Compound [HRC]) were monitored as measures of substrate efficiency in aquifer microcosms spiked with trichloroethene (TCE). In long-term experiments, the fermentation of PRB substrates to slow-degrading organic acids maintained low H₂ partial pressures (≤ 10^?3.5) that, as previous studies suggest, may give competitive advantage to dechlorinators over hydrogenotrophic methanogens. Whey-amended and lactate-amended microcosms exhibited faster complete dechlorination and, according to organic acid carbon flow, higher rates of fermentation to acetate. In HRC-amended microcosms, propionate appeared to serve as a carbon sink that prolonged dechlorination. Upon complete dechlorination, whey microcosms contained the highest percentage of organic acid carbon. Native Dehalococcoides populations increased by 3 orders of magnitude (per g sediment) in whey-amended microcosms. Whey's efficiency improved in microcosms prepared with aquifer sediment and water from within a downgradient whey PRB. Results suggested whey loading values of 0.2 kg/m³ may be appropriate under sufficiently reducing conditions to efficiently stimulate hydrogenotrophic and potentially actetotrophic dechlorinating populations. Renewal of whey PRBs may, however, be required. Implications for further long-term study of cost-efficiencies are discussed.     

零价铁对2,4-二氯酚生物还原脱氯的影响研究

采用间歇试验, 接种驯化两月的厌氧混合微生物, 考察厌氧体系中添加零价铁(Fe0)对2,4-二氯酚(2,4-DCP)生物还原脱氯效果的影响, 并对影响“Fe0+微生物”体系的一些因素进行了探索。结果显示：与零价铁或微生物的单独作用相比, “Fe0+微生物”体系能够有效促进2,4-DCP的脱氯反应, 最佳Fe0投加量和微生物接种量分别为0.5 g/L和376.2 mgVSS/L; 初始pH = 8.0对2,4-DCP的转化效果最好, 偏酸性环境不利于污染物转化; 微生物接种量与铁用量之间有一适宜比例, 一定范围内增加微生物接种量可催生出更多可降解污染物的酶或酶系, 提高2,4-DCP的降解效果。     

零价铁对2,4-二氯酚生物还原脱氯的影响研究

采用间歇试验,接种驯化两月的厌氧混合微生物,考察厌氧体系中添加零价铁（Fe^0）对2,4-二氯酚（2,4-DCP）生物还原脱氯效果的影响,并对影响“Fe^O＋微生物”体系的一些因素进行了探索。结果显示：与零价铁或微生物的单独作用相比,“Fe^O＋微生物”体系能够有效促进2,4-DCP的脱氯反应,最佳Fe^O投加量和微生物接种量分别为0.5g／L和376.2mgVSS／L;初始pH=8.0对2,4-DCP的转化效果最好,偏酸性环境不利于污染物转化;微生物接种量与铁用量之间有一适宜比例,一定范围内增加微生物接种量可催生出更多可降解污染物的酶或酶系,提高2,4-DCP的降解效果。     

Molecular characterization of microbial populations at two sites with differing reductive dechlorination abilities

This study compares three molecular techniques, including terminal restriction fragment length polymorphism (T-RFLP), RFLP analysis with clone sequencing, and quantitative PCR (Q-PCR) for surveying differences in microbial communities at two contaminated field sites that exhibit dissimilar chlorinated solvent degradation activities. At the Idaho National Engineering and Environmental Laboratory (INEEL), trichloroethene (TCE) was completely converted to ethene during biostimulation with lactate. At Seal Beach, California, perchloroethene (PCE) was degraded only to cis-dichloroethene (cDCE) during biostimulation but was degraded to ethene after bioaugmentation with a dechlorinating culture containing Dehalococcoides strains. T-RFLP analysis showed that microbial community composition differed significantly between the two sites, but was similar within each site among wells that had low or no electron donor exposure. Analysis of INEEL clone libraries by RFLP with clone sequencing revealed a complex microbial population but did not identify any Dehalococcoides strains. Q-PCR targeting the 16S rRNA gene of Dehalococcoides strains – known for their unique capability to dechlorinate solvents completely to ethene – revealed a significant population at INEEL, but no detectable population at Seal Beach prior to bioaugmentation. Detection of Dehalococcoides by Q-PCR correlated with observed dechlorination activity and ethene production at both sites. Q-PCR showed that Dehalococcoides was present in even the pristine well at INEEL, suggesting that the difference in dechlorination ability at the two sites was due to the initial absence of this genus at Seal Beach. Of the techniques tested, Q-PCR quantification of specific dechlorinating species provided the most effective and direct prediction of community dechlorinating potential.     

Biodegradation of 3-chlorobenzoate by Pseudomonas putida 10.2

Pseudomonas putida 10.2, a 3-chlorobenzoate (3CBa)-degrading bacterium, was isolated from a soil sample obtained from an agricultural area in Chiang Mai, Thailand. This bacterium could degrade 2mm 3CBa very rapidly with the concomitant formation of chloride ion when grown in mineral salt-yeast extract medium. The presence of glucose, lactose and pyruvate in the medium reduced the capability of this bacterium to degrade 3CBa. Metabolites such as 3-chlorocatechol (3CC), catechol and cis,cis-muconic acid (muconate) could be detected in the growth medium or in cell suspensions when 3CBa was used as the substrate. Furthermore, when crude enzyme extract prepared from 3CBa-grown P. putida 10.2 was incubated with 3CC, catechol and muconate could be detected in the reaction mixtures. Thus, the biodegradation pathway of 3CBa by P. putida 10.2 was proposed to involve transformation of 3CBa to 3CC. The dehalogenation step is believed to involve removal of chloride from 3CC to form catechol, which is subsequently converted to muconate.     

Reductive Dechlorination of Tetrachloroethene Following Abiotic Versus Biotic Reduction of Hexavalent Chromium

A feasibility evaluation identified chemical reduction and biostimulation as a potential remedy for a plume containing hexavalent chromium (Cr(VI)) and tetrachloroethene (PCE) at an industrial site in southern California. The objectives of this laboratory study were to determine the stoichiometry of calcium polysulfide (CaS_x) reaction with Cr(VI) in the presence of sediment, the effect of CaS_x on the potential for in situ biological reductive dechlorination of PCE, and the potential to reduce Cr(VI) and PCE by addition of only an electron donor. Approximately 1 L of CaS_x solution (containing 50 g S^2-/L) was required per 1000 L of groundwater containing 45 mg/L of Cr(VI) (i.e., 1.8 mol S^2- per mol Cr(VI)). The sediment also exerted a sulfide demand (≥0.38 g S^{2 -} per kg sediment), but at a slower rate than the Cr(VI). In microcosms prepared with lactate, corn syrup, soybean oil, or methanol, but no CaS_x, the Cr(VI) was biologically reduced in the treatments with lactate and corn syrup, but much more slowly than with CaS_x. Even after 20 months of incubation, no significant reductive dechlorination of PCE occurred in any of the microcosms, including those in which the Cr(VI) was removed with CaS_x. Bioaugmentation was tested with the microcosms that received lactate and corn syrup (following 20 months of incubation), using an enrichment culture that actively dechlorinates trichloroethene. PCE dechlorination began within 1 month in the lactate-only treatment; in the corn syrup-amended treatment, PCE dechlorination occurred in only one of the three bottles. However, no PCE dechlorination occurred following bioaugmentation of the lactate and corn syrup microcosms that were initially treated with CaS_x, indicating that CaS_x (and/or its reaction products) exerted a negative impact on the chlororespiring microbes. This outcome highlights the need to evaluate sites on a case-by-case basis when in situ chemical treatment is applied prior to microbial reductive dechlorination.     

Environmental distribution of the trichloroethene reductive dehalogenase gene (tceA) suggests lateral gene transfer among Dehalococcoides

The trichloroethene reductive dehalogenase gene (tceA) of Dehalococcoides spp. was detected in 12 of 21 trichloroethene-to-ethene dechlorinating enrichment cultures established from aquifer and sediment samples collected from diverse geographic locations in the USA. Analysis of the tceA chromosomal regions indicated that the tceA genes shared greater than 95% sequence identity, and all shared identical tceAB spacer sequences and tceB genes downstream of tceA. A putative transposable element (PTE) was present 1077 bp downstream of the tceB stop codon in three of eight chromosomal regions analyzed. Sequence identity was interrupted downstream of tceB and upstream or downstream of the PTE, suggesting that intrachromosomal or interchromosomal transfer of tceAB had occurred.     

Fe(III) Oxide Reduction by a Gram-positive Thermophile: Physiological Mechanisms for Dissimilatory Reduction of Poorly Crystalline Fe(III) Oxide by a Thermophilic Gram-positive Bacterium Carboxydothermus ferrireducens

Physiological strategies driving the reduction of poorly crystalline Fe(III) oxide by the thermophilic Gram-positive dissimilatory Fe(III)-reducing bacterium C. ferrireducens were evaluated. Direct cell-to-mineral contact appears to be the major physiological strategy for ferrihydrite reduction. This strategy is promoted by cell surface-associated c-type cytochromes, and the extracellular electron transfer to ferrihydrite is linked to energy generation via a membrane-bound electron transport chain. The involvement of pili-like appendages in ferrihydrite reduction has been detected for the first time in a thermophilic microorganism. A supplementary strategy for the utilization of a siderophore (DFO) in dissimilatory ferrihydrite reduction has also been characterized.     

Fe(III) Reducing Microorganisms from Iron Ore Caves Demonstrate Fermentative Fe(III) Reduction and Promote Cave Formation

The banded iron formations (BIF) of Brazil are composed of silica and Fe(III) oxide lamina, and are largely covered by a rock cap of BIF fragments in a goethite matrix (canga). Despite both BIF and canga being highly resistant to erosion and poorly soluble, >3,000 iron ore caves (IOCs) have formed at their interface. Fe(III) reducing microorganisms (FeRM) can reduce the Fe(III) oxides present in the BIF and canga, which could account for the observed speleogenesis. Here, we show that IOCs contain a variety of microbial taxa with member species capable of dissimilatory Fe(III) reduction, including the Chloroflexi, Acidobacteria and the Alpha- Beta- and Gammaproteobacteria; however, Fe(III) reducing enrichment cultures from IOCs indicate the predominance of Firmicutes and Enterobacteriaceae, despite varying the carbon/electron donor, Fe(III) type, and pH. We used model-based inference to evaluate multiple candidate hypotheses that accounted for the variation in medium chemistry and culture composition. Model selection indicated that none of the tested variables account for the dominance of the Firmicutes in these cultures. The addition of H₂ to the headspace of the enrichment cultures enhanced Fe(III) reduction, while addition of N₂ resulted in diminished Fe(III) reduction, indicating that these Enterobacteriaceae and Firmicutes were reducing Fe(III) during fermentative growth. These results suggest that fermentative reduction of Fe(III) may play a larger role in iron-rich environments than expected. Our findings also demonstrate that FeRM are present within the IOCs, and that their reductive dissolution of Fe(III) oxides, combined with mass transport of solubilized Fe(II) by groundwater, could contribute to IOC formation.     

Bacterial Reduction of Cr(VI) and Fe(III) in In Vitro Conditions

ABSTRACT Chemical reduction of Cr(VI) can be a strategy to detoxify toxic metals in oxidized states, whereas reduction of Fe(III) could enhance the availability of Fe in the form of Fe(II) to boost plant growth. However, it creates another problem of chemical sludge disposal. Hence, microbial conversion of Cr(VI) to Cr(III) and Fe(III) to Fe(II) is preferred over the chemical method. Out of 11 bacterial strains isolated from the rhizospheric zone of Typha latifolia growing on fly ash dump sites, four isolates were selected for the reduction of Cr(VI) and Fe(III) and were identified as Micrococcus roseus NBRFT2 (MTCC 9018), Bacillus endophyticus NBRFT4 (MTCC 9021), Paenibacillus macerans NBRFT5 (MTCC 8912), and Bacillus pumilus NBRFT9 (MTCC 8913). These strains were individually tested for survival at different concentrations of Cr(VI) and Fe(III), pH, and temperature, and then, their ability for reduction of both metals was evaluated at optimum pH 8.0 and temperature 35°C. The results indicated that NBRFT5 was able to reduce the maximum amount, 99% Cr(VI) and 98% Fe(III). Other strains also reduced these metals to different levels, but less than NBRFT5. Hence, these strains may be used for decontamination of metal-contaminated sites, particularly with Cr(VI) and Fe(III) through the reduction process.     

Interactions Between Fe(III)-oxides and Fe(III)-phyllosilicates During Microbial Reduction 2: Natural Subsurface Sediments

Dissimilatory microbial reduction of solid-phase Fe(III)-oxides and Fe(III)-bearing phyllosilicates (Fe(III)-phyllosilicates) is an important process in anoxic soils, sediments and subsurface materials. Although various studies have documented the relative extent of microbial reduction of single-phase Fe(III)-oxides and Fe(III)-phyllosilicates, detailed information is not available on interaction between these two processes in situations where both phases are available for microbial reduction. The goal of this research was to use the model dissimilatory iron-reducing bacterium (DIRB) Geobacter sulfurreducens to study Fe(III)-oxide vs. Fe(III)-phyllosilicate reduction in a range of subsurface materials and Fe(III)-oxide stripped versions of the materials. Low-temperature (12 K) Mossbauer spectroscopy was used to infer changes in the relative abundances of Fe(III)-oxide, Fe(III)-phyllosilicate, and phyllosilicate-associated Fe(II) (Fe(II) phyllosilicate). A Fe partitioning model was employed to analyze the fate of Fe(II) and assess the potential for abiotic Fe(II)-catalyzed reduction of Fe(III)-phyllosilicates. The results showed that in most cases Fe(III)-oxide utilization dominated (70–100%) bulk Fe(III) reduction activity, and that electron transfer from oxide-derived Fe(II) played only a minor role (ca. 10–20%) in Fe partitioning. In addition, the extent of Fe(III)-oxide reduction was positively correlated to surface area-normalized cation exchange capacity and the Fe(III)-phyllosilicate/total Fe(III) ratio. This finding suggests that the phyllosilicates in the natural sediments promoted Fe(III)-oxide reduction by binding of oxide-derived Fe(II), thereby enhancing Fe(III)-oxide reduction by reducing or delaying the inhibitory effect that Fe(II) accumulation on oxide and DIRB cell surfaces has on Fe(III)-oxide reduction. In general our results suggest that although Fe(III)-oxide reduction is likely to dominate bulk Fe(III) reduction in most subsurface sediments, Fe(II) binding by phyllosilicates is likely to play a key role in controlling the long-term kinetics of Fe(III) oxide reduction     

Fe(III)的微生物异化还原

异化Fe(III)还原微生物是厌氧环境中广泛存在的一类主要微生物类群,它们的共同特征是可以利用Fe(III)作为末端电子受体而获能。异化Fe(III)还原微生物具有强大的代谢功能,可还原许多有毒重金属包括一些放射性核素,还可降解利用许多有机污染物,在污染环境的生物修复中具有重要的应用价值。本文对异化Fe(III)还原微生物的分布、分类,代谢功能多样性以及异化Fe(III)还原的意义做了评述,旨在加强相关领域的研究人员对此的了解和重视,通过学科的交叉和合作加快我国在这一领域的研究。     

Factors controlling the carbon isotope fractionation of tetra- and trichloroethene during reductive dechlorination by Sulfurospirillum ssp. and Desulfitobacterium sp. strain PCE-S

Carbon stable isotope fractionation of tetrachloroethene (PCE) and trichloroethene (TCE) was investigated during reductive dechlorination. Growing cells of Sulfurospirillum multivorans, Sulfurospirillum halorespirans, or Desulfitobacterium sp. strain PCE-S, the respective crude extracts and the abiotic reaction with cyanocobalamin (vitamin B(12)) were used. Fractionation of TCE (alphaC=1.0132-1.0187) by S. multivorans was more than one order of magnitude higher than values previously observed for tetrachloroethene (PCE) (alphaC=1.00042-1.0017). Similar differences in fractionation were observed during reductive dehalogenation by the close relative S. halorespirans with alphaC=1.0046-1.032 and alphaC=1.0187-1.0229 for PCE and TCE respectively. TCE carbon isotope fractionation (alphaC=1.0150) by the purified PCE-reductive dehalogenase from S. multivorans was more than one order of magnitude higher than fractionation of PCE (alphaC=1.0017). Carbon isotope fractionation of TCE by Desulfitobacterium sp. strain PCE-S (alphaC=1.0109-1.0122) as well as during the abiotic reaction with cyanocobalamin (alphaC=1.0154) was in a similar range to previously reported values for fractionation by mixed microbial cultures. In contrast with previous results with PCE, no effects due to rate limitations, uptake or transport of the substrate to the reactive site could be observed during TCE dechlorination. Our results show that prior to a mechanistic interpretation of stable isotope fractionation factors it has to be carefully verified how other factors such as uptake or transport affect the isotope fractionation during degradation experiments with microbial cultures.     

2-bromoethanesulfonate (BES) Enhances Sulfate-reducing Bacterial Population and Dichlorodiphenyltrichloroethane (DDT) Dechlorination in an Anaerobic Paddy Soil

2-bromoethanesulfonate (BES) is a structural analogue of 2-mercaptoethanesulfonic acid (coenzyme M) and often used to specifically inhibit methanogenesis. The role of BES and sulfate on the reductive dechlorination of dichlorodiphenyltrichloroethane (DDT) was compared in an anaerobic soil slurry reactor of sulfate-reducing system in this study. The population of soil sulfate-reducing bacteria (SRB) was markedly decreased under DDT condition compared to DDT-free reactor, while greatly increased by sulfate and slightly increased by BES. However, the dechlorination rate of DDT was the highest in the DDT+BES treatment, followed in order by DDT+Sulfate and the control condition. In the DDT+BES treatment, more than 60% of DDT-Cl was cleaved within 16 weeks, which was about 124% and 369% greater than that in the DDT+Sulfate treatment and under the control condition, respectively. The results suggested that the inhibition of methanogenesis by BES was another pathway to improve sulfate-reducing activity and the related dechlorination rate of DDT in waterlogged soils.     

Biological Control of Hog Waste Odor through Stimulated Microbial Fe(III) Reduction

Odor control and disposal of swine waste have inhibited expansion of swine production facilities throughout the United States. Swine waste odor is associated primarily with high concentrations of volatile fatty acids (VFAs). Here, we demonstrate that stimulated Fe(III) reduction in hog manure can rapidly remove the malodorous compounds and enhance methane production by 200%. As part of these studies, we enumerated the indigenous Fe(III)-reducing population in swine waste and identified members of the family Geobacteraceae as the dominant species. These organisms were present at concentrations as high as 2 × 10⁵ cells g⁻¹. Several pure cultures of Fe(III) reducers, including Geobacter metallireducens, Geobacter humireducens, Geobacter sulfurreducens, Geobacter grbiciae, Geothrix fermentans, and Geovibrio ferrireducens, readily degraded some or all of the malodorous VFAs found in swine manure. In contrast, Shewanella algae did not degrade any of these compounds. We isolated an Fe(III) reducer, Geobacter strain NU, from materials collected from primary swine waste lagoons. This organism degraded all of the malodorous VFAs tested and readily grew in swine waste amended with Fe(III). When raw waste amended with Fe(III) was inoculated with strain NU, the VFA content rapidly decreased, corresponding with an almost complete removal of the odor. In contrast, the raw waste without Fe(III) or strain NU showed a marked increase in VFA content and a rapid pH drop. This study showed that Fe(III) supplementation combined with appropriate bioaugmentation provides a simple, cost-effective approach to deodorize and treat swine waste, removing a significant impediment to the expansion of pork production facilities.